Macro-mechanical properties of saturated sandstone of Jushan Mine under post-peak cyclic loading: an experimental study

The mechanical properties of rocks are greatly affected by water action. Many underground structures can be failed by changes in the water environment. To reveal the mechanical properties of the rocks after saturation, a series of saturated sandstones are prepared to study the changes in the mechanical properties during post-peak cyclic loading and unloading. The results show that the strength characteristics of the sandstones decrease after saturation. There is an exponential function between the peak strength and the damage degree and between the crack damage stress and the damage degree. A new method for calculating the elastic modulus is proposed. The results of both calculation methods show that the elastic modulus of the saturated sandstones decreases. The relationship between the elastic modulus obtained by the two methods and the damage degree is quite different. After saturation, the dilatancy of the sandstones increases in the post-peak stage. The volumetric strain, the plastic shear strain, and the peak dilatancy angle all increase with increasing damage degree. Because of the filling by water molecules, the P-wave velocity increases. There is an exponential function relationship between the P-wave velocity and the damage degree. Because of the softening after saturation, more macroscopic failure cracks and fracture surfaces will be formed in the saturated sandstones. The research results of this paper can provide some guidance for excavation and engineering design in water-rich rock.